Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$155.54	10.236%	$171.4611	$171.46	$171.45	$171.50
Purchase #2	$168.30	5.460%	$177.4892	$177.49	$177.50	$177.50
Purchase #3	$226.33	6.580%	$241.2225	$241.22	$241.20	$241.20
Purchase #4	$234.29	13.284%	$265.4131	$265.41	$265.40	$265.40
Purchase #5	$195.98	13.709%	$222.8469	$222.85	$222.85	$222.80
Purchase #6	$38.46	10.597%	$42.5356	$42.54	$42.55	$42.50
Purchase #7	$59.86	10.811%	$66.3315	$66.33	$66.35	$66.30
7 purchase totals =	$1,078.76		$1,187.2999	$1,187.30	$1,187.30	$1,187.20